Hacker News Reader

Comment by MrHamburger | Hacker News Reader

> The OS receives the devicetree in a memory location

Which memory location? Any ARM SoC does not have defined where RAM must be. So which address are you going to touch from your OS to get the configuration? Yep, that's exactly what UEFI and ACPI are for

And no "at the end of kernel image" is not a memory location, because then your solution works only with your specific ad-hoc setup. All the Linux distros are not working, BSD is not working, Windows is not working. Only your blessed Linux Kernel will work and that's going to be all. No difference from adding a device tree directly into a Kernel then.

View on HN

> Which memory location?

> And no "at the end of kernel image" is not a memory location

Like @201984 said, u-boot can load the devicetree separately and this is the more common way to boot. But even if it didn't, "the end of the kernel image" actually is a memory location. Kernel knows where it's executing from (all CPUs, not just ARM, have the Program Counter register) and it's own size (kernel decompressor knows the end of the compressed data).

> Any ARM SoC does not have defined where RAM must be.

That's known from the devicetree.

> All the Linux distros are not working, BSD is not working, Windows is not working.

False. You can take Ubuntu as example. There's only one bootable image for all ARM64. I have no experience with BSD and who tf. cares about Windows?

Again, works only for your ad-hoc solution, you never want a lower layer to know anything about upper layer, that's why upper layer (OS) talks to lower layer via UEFI and ACPI

Which demonstrates again that you don't know how UEFI and ACPI works and how dangerous they are.

> Which memory location?

The location of the device tree is given to the kernel in x0 by the boot loader. See https://docs.kernel.org/arch/arm64/booting.html.

This device tree has information about the RAM location and hardware on the device, so in theory this can work just as well as ACPI does.

Which will work only for a Linux, everything else won't boot on your ad-hoc solution.

A quick Google shows that BSD supports devicetree too. So that leaves... Windows? Don't tell me you're a Windows fan?? That would explain why you love ring -2 binary blobs too.

Reply on news.ycombinator.com